1. Field of the Invention
The present invention relates to a method of processing a waste catalyst of an internal-combustion engine that has a metal cover connected to exhaust gas pipes, a catalyst carrier, and a γ-alumina coating film containing precious metals supported on the catalyst carrier. By this method, a precious metal concentrate can be separated from the other components, the components of the waste catalyst can be reused, and precious metal collecting can be performed through a copper smelting procedure and a precious metal collecting procedure.
2. Description of the Related Art
Conventionally, to purify exhaust gas, especially exhaust gas of the internal-combustion engine of an automobile, a metallic or ceramic catalyst carrier is used, as shown in FIGS. 1A through 3. A metal cover 10 attached to exhaust gas pipes 9 and 12 shown in FIG. 3 has a metallic or ceramic catalyst carrier provided therein. As shown in FIGS. 2A and 2B, the metallic or ceramic catalyst carrier is coated with a γ-alumina coating film 6 that is impregnated with precious metals 7 to serve as catalysts, such as platinum, palladium, or rhodium.
A metallic catalyst carrier can overcome the problems of poor starting characteristics at a cool temperature (or an ordinary temperature) and poor shock resistance that are often seen with a ceramic catalyst carrier. Therefore, more and more metallic catalyst carriers are being used in recent years.
The waste catalysts of an internal-combustion engine are accompanied by connection engaging pipes and the metal cover 10 having at least a pair of an input engaging pipe and an outlet engaging pipe, as shown in FIG. 3. The metal cover 10 covers a layer-type catalyst carrier 5 or a honeycomb-type catalyst carrier 8, as shown in FIGS. 2A and 2B. Also, the precious metals 7 as catalyst materials and the thin γ-alumina coating film 6 are provided on the surface of the catalyst carrier, as shown in FIGS. 2A and 2B.
The metal covers 10 and 2 and the exhaust gas pipes 9 and 12 shown in FIGS. 1A and 1B and FIGS. 3A and 3B are normally made of high-grade steel or nonmagnetic ferroalloy.
The metallic catalyst carrier 1 shown in FIG. 1A is made of a very thin ferromagnetic Fe—Cr—Al alloy. Carrier foil 3 that forms each layer is molded in a smooth form and a wave form alternately. Each peak of the waves is brought into contact with the foil of the adjacent layer, and can be joined to the foil by spot welding. The surface of the γ-alumina coating film 6 on the metallic catalyst carrier 1 is impregnated with the precious metals 7.
The ceramic catalyst carrier 4 shown in FIG. 1B is made of cordierite (2MgO—2Al2O3—5SiO2), and takes the honeycomb form 8, as shown in FIG. 2B. In the ceramic catalyst carrier 4, the surface of the γ-alumina coating film 6 is also impregnated with the precious metals 7.
The foil 3 of the metallic catalyst carrier 1 is as thin as 20 μm to 30 μm, and has a small heat capacity. Accordingly, the metallic catalyst carrier can be quickly heated by exhaust gas of the internal-combustion engine, and a catalytic effect starts appearing only a short time after the internal-combustion engine is activated. Being not greatly affected by mechanical or thermal impact, the metallic catalyst carrier 1 can be provided in a closer position to the engine than the catalysts in a ceramic catalyst carrier in the exhaust pipe. Accordingly, the heating can be quickly carried out.
However, it is extremely difficult to separate the γ-alumina coating film and the precious metals from the foil of a metallic catalyst carrier. As a result, most metallic catalyst carriers are scrapped, and the precious metals are not recovered.
Among catalyst carriers, ceramic catalyst carriers are mechanically separated from automobiles that are being scrapped, and catalytic materials such as platinum, palladium, and rhodium, are recovered.
The materials to be separated are the catalysts used in internal-combustion engines to be scrapped. The recovering of waste catalysts from an internal-combustion engine is not necessarily performed with a desired precision. As a result, mechanically damaged catalysts or catalysts still connected to a damaged connecting engaging pipe or exhaust gas pipes are often delivered as goods.
Japanese Unexamined Patent Publication No. 2000-248322, titled “Method of Recovering Platinum Group Element from Metal Substrate Catalyst”, discloses a method of processing a metallic catalyst carrier, with a metal cover remaining the metallic catalyst carrier. In this prior art, a catalyst that is impregnated with precious metals is heated together with a metal cover in an electric furnace, so that the precious metal is absorbed by copper, and that the copper is oxidized to concentrate and recover the precious metals. The metal cover and the magnetic carrier foil, such as Fe—Cr—Al alloy foil, are oxidized and then discharged as slag.
Japanese Patent Publication No. 2645789, titled “Method of and Apparatus for Recycling Catalytic Converters”, also discloses a method of separating a metallic catalyst carrier. In this method, an impact-type crusher is combined with a pneumatic separation system. Each metallic catalyst carrier is disassembled to various pieces that can be recycled as usable components at the stage of delivery. The components used for recovering precious metals contain catalytic precious metals at a high concentration. Accordingly, this method of separating a metallic catalyst carrier involves neither chemicals nor toxic substances.
In the prior art disclosed in Japanese Unexamined Patent Publication No. 2000-248322, however, the γ-alumina containing the precious metals supported on a metallic catalyst carrier is not removed from the Fe—Cr—Al alloy foil, and the metal cover is not removed either. It is therefore necessary to oxidize and dissolve the Fe—Cr—Al alloy foil and the metal cover. As a result, a large quantity of slag is generated, and, compared with a case of processing a ceramic catalyst carrier, higher process costs are required.
In the prior art disclosed in Japanese Patent Publication No. 2645789, the impact-type crushing is performed in one step. In this manner, a metal cover that is not easily crushed and a metallic catalyst carrier that can be easily crushed are subjected to crushing at the same time, resulting in a poor crushing efficiency. Furthermore, with a fixed discharging screen of an impact type, the fragments of the metal cover that is made of high-grade steel or nonmagnetic ferroalloy containing nickel are deformed into round shapes. As a result, it becomes difficult to prevent contamination of the metallic catalyst carrier containing precious metals.